Python process CPU usage going high suddenly. how to detect the place?

Question

I run multiple (400 python simultaneously) I start new one each 1.5 sec and repeat round robin I found that sometimes my CPU usage goes 100%

While sometimes it is as low as 30%-50%

I need to understand what push it so high, is it the process creation time ? What should I do to check and debug the spot?

NOTE: it seems that on steady state where all 400 are running each take 0.2% cpu, so it is only the first 4 seconds of the process, I added a dealy when cput is high.